1. Field of the Invention
The present invention relates to eye glasses and more particularly relates to improved arrangements for attachment of a second or auxiliary pair of lenses to such eye glasses. More particularly, the invention relates to the provision of mutually cooperating and interfitting projections on primary and auxiliary or secondary lenses enabling the releasable mechanical engagement between the primary and secondary lenses.
2. Description of Related Art
Wearers of eye glasses often choose to attach a second set of lenses to those eye glasses to provide sunshade and ultra violet eye protection. This prevents having to keep a separate pair of sun glasses and it also means the wearer can still derive the visual acuity from the prescription lenses whilst deriving the benefits of sun glasses. There are already in existence various clip on secondary lenses for detachable fixation to a primary pair of lenses such that the latter are instantly converted into sung glasses. Means of attachment of the secondary lenses has in the past taken various forms. One version employs clips which engage a bridge on the primary spectacles.
Another arrangement for detachably attaching a secondary pair of lenses to a pair of primary spectacles is described in Australian patent 684423. The patent discloses an eye glass comprising a spectacle frame support for supporting primary lenses including side portions each having an extension for pivotally coupling a leg means and two rear side portions each having a protection secured thereto. The primary spectacle frame also including an upper side portion and a pair of first magnetic members secured in the projections. The eye glasses further comprise an auxiliary spectacle frame for supporting auxiliary lenses including two side portions each having an arm extending therefrom for extending over and for engaging with the upper side portion of the primary spectacle frame such that the auxiliary lenses are held against the primary spectacle frame by means of the magnetic members.
Whilst the clip arrangements and magnetic interengagement works to secure the auxiliary lenses to the primary frame, these methods suffer from a number of disadvantages. The clip arrangement is cumbersome, heavy and unattractive and according to some versions can lead to scratching of the primary lenses when the auxiliary lenses is fitted to the primary spectacle frame. The magnetic arrangements described in Australian patent 684423 have also been disclosed in U.S. Pat. No. 5,416,537 to Sadler and U.S. Pat. No. 5,568,207 by Richard Chao. One of the problems with the magnetic arrangements is that in time the magnetism degrades, dramatically reducing the effectiveness of the interfitting. Even where the magnetism is at its strongest when the frames are first manufactured, the magnetic forces may not be enough made to withstand dynamic loading which may be placed on the auxiliary frames particularly where the user is engaged in sports such as jogging, jumping, tennis and other like activities. When a user is engaged in vigorous exercise the auxiliary spectacle frame can be instantly released from the primary spectacle frames leading to damage of the auxiliary spectacle frames and inconvenience to the user.
In addition, the magnetic surface in the projections on the primary frame may be prone to corrosion and rust, degrading magnetic effectiveness. A further problem is that where the auxiliary frames are not released from the primary spectacle frames, they can move on the primary frames as the magnetic surfaces allow a range of movement over the surface area of the magnet. This has the disadvantage of increasing the gap between the auxiliary frames and the primary spectacles allowing sun light to penetrate through the lenses in the primary spectacle frames reducing the overall effectiveness of the interengagement between the auxiliary lenses and the primary spectacle lenses.